The present invention relates to devices useful for diagnosing visual system diseases, and in particular to a computerized device for screening anterior visual system diseases utilizing the Pulfrich effect.
The Pulfrich effect is a stereo-illusion effect which occurs in patients with a degree of impairment in one eye. A pendulum moving perpendicular to the line of sight is presented to the patient. Normally the pendulum appears to the patient to move linearly. However, if one eye is affected by anterior visual system disease, a stereo-illusion causes the pendulum to appear to move in an ellipse. The elliptical motion of the pendulum is clockwise if the left eye is affected and counter-clockwise if the right eye is affected.
The degree of impairment may be assessed by utilizing neutral density filters of varying density in front of the less impaired eye. When filters of appropriate density are chosen, the stereo-illusion effect disappears.
The Pulfrich effect has been employed to test for anterior visual system disease utilizing actual pendulums. For example, the prior art discloses the use of bulky mechanical pendulums, such as disclosed in U.S. Pat. No. 5,099,858 to Hofeldt. Hofeldt '858 discloses a device for diagnosing ocular and optic nerve disease utilizing the Pulfrich effect comprising an enclosure with two eyepieces, a pendulum bob and a reference point for the bob. Hofeldt '858 also provides means for varying the light perceived through each of the eyepieces.
U.S. Pat. No. 5,347,330 also issued to Hofeldt discloses the use of an audio/visual recording showing a figure moving in a pendulum-like fashion to produce the Pulfrich effect. In order to use this device, the person being tested views the audio/visual recording through a device which sequentially provides filters of varying density.
While the prior art discloses the use of the Pulfrich stereo-illusion effect to test for anterior visual system disease, the mechanisms suggested in the prior art are not suitable for many classes of patients, such as pre-verbal children or supine patients.
These and other limitations of the prior art are overcome by the present invention.